1. Field of Invention
The invention relates to a sheet-supply device that supplies sheets, one by one, from a stack of sheets held in an inclined position by a hopper portion, by rotation of a sheet-supply roller and a printing device including the sheet-supply device. More particularly, the invention pertains to a sheet-supply device that can smoothly convey a last one sheet in a direction reverse to a sheet feed direction without any interference.
2. Description of Related Art
Typically, various recording devices, such as printers and facsimile machines, include a sheet-supply device that supplies sheets, which are held by a hopper portion, one by one, by rotation of a sheet-supply roller. Two types of sheet-supply devices are practical in use. One type of sheet-supply device holds a plurality of sheets in a horizontal position, and another type of the sheet-supply devices holds a plurality of sheets in an inclined position. Recently, the latter type of sheet-supply device has been mostly adopted to save installation space. The inclined-type sheet-supply device is generally provided with a friction pad having a high coefficient of friction, near a lower end of an inclined wall that supports the sheets loaded thereon from their underside.
That is, because a multi-feed problem (two or more sheets are supplied at a time) often occurs during a sheet feed operation when the amount of remaining sheets is low, the friction pad is provided under the sheets pressed by the sheet-supply roller. By doing so, a lowermost sheet, which contacts the friction pad, is prevented from moving in a sheet feed direction due to the frictional resistance produced by the friction pad. In addition, sheets, except a topmost sheet, are also prevented from moving in the sheet feed direction because of a frictional resistance between adjacent sheets. Thus, only the topmost sheet, contacting the sheet-supply roller, is separated and supplied from the stack of sheets. Therefore, as described above, the multi-feed problem can be prevented.
In the sheet-supply device, the fed sheet is further conveyed by a pair of conveyor rollers, which are provided downstream of the sheet-supply device, to a recording unit, which is provided downstream of the conveyor rollers in the sheet feed direction. Commonly, any deviation of the sheet is corrected by the conveyor rollers. Although a drive mechanism is also involved in the correction of a sheet deviation, explanations for the correction are given without describing the operation of the drive mechanism. The correction is generally performed as described below. One method is that a sheet, which is supplied from the sheet-supply device, is thrust against the conveyor rollers so that a leading edge of the sheet contacts a nip point of the conveyor rollers and becomes bent when the conveyor rollers are not rotated, and thereafter the conveyor rollers are rotated to correct the deviation of the sheet.
Another method is as described below. A sheet is supplied by the sheet-supply device while a pair of conveyor rollers are being rotated. After a leading edge of the sheet is pinched by the pair of conveyor rollers, the rotation of the conveyor rollers is stopped. Then, the conveyor rollers are rotated in a direction reverse to the sheet feed direction until the leading edge of the sheet becomes free from the pinching of the conveyor rollers. Upon the disengagement of the leading edge of the sheet from the conveyor rollers, the reverse rotation of the conveyor rollers is stopped. Then, again, the conveyor rollers are rotated in the direction to feed the sheet to correct the deviation of the sheet.
The former method requires a drive mechanism that can separately perform the sheet feed operation and the driving of the conveyor rollers. The latter method requires a sheet feed mechanism that can convey a sheet in the reverse direction toward the hopper portion.
As described above, the friction pad, which applies a frictional resistance to the sheets, is fixedly provided near the lower end of the inclined wall in order to prevent the multi-feed problem when the amount of remaining sheets is low. However, due to types and/or sizes of sheets to be loaded, the friction pad may not apply a sufficient frictional resistance to the sheets to avoid the multi-feed problem.
In addition, the friction pad slightly protrudes from an upper surface of the inclined wall in order to effectively apply its frictional resistance to the sheets. In a case where a small-sized rigid sheet, such as a postcard, is supplied from the sheet-supply device and its deviation is corrected by the latter method described above, the sheet may pass over the friction pad or a trailing edge of the sheet barely contacts the friction pad. When the conveyor rollers are rotated in the reverse direction to feed the sheet back from this condition, the trailing edge of the sheet may dig into the friction pad or the sheet may be caught between the sheet-supply roller and the friction pad with a result of being bent into a V-shape.
As a result, a static friction with respect to the small sheet by the sheet-supply roller and the friction pad becomes large, so that various problems occur. For example, a sheet fed back in the reverse direction is bent because the sheet cannot be stably conveyed in the reverse direction, and a printing area is shifted toward the trailing edge of the sheet because the small sheet cannot be precisely conveyed in the reverse direction by a predetermined amount.